Process RDF from Input. Input is either an atom or a term of the
format stream(Handle). For each encountered description, call
OnObject(+Triples) to handle the triples resulting from the
description. Defined Options are:

base_uri(+URI)

Determines the reference URI.

db(DB)

When loading from a stream, the source is taken from
this option or -if non-existent- from base_uri.